For automated haemo-dynamometry, it is required to first pressurize an arm or wrist cuff with air, and to subsequently release the pressure-usually step-by-step. During the individual steps, the pressure within the cuff and heart beat are measured to determine the blood pressure according to the oscillometric method.
For the stepwise release of the pressurized air, usually solenoid valves are used that are connected to the cuff. In particular, in mobile haemo-dynamometric apparatuses that are operated off-line, it is necessary to keep power consumption to a minimum. It is also desirable to minimize the weight of the valve; thus the total weight of the apparatus can be reduced.
Solenoid valves are known that, via an armature and against the force of a spring, actuate a piston contained in a valve body, the free end of which features a seal for sealing the channel. Such valves feature a relatively large moving mass that results in a proportionately large power consumption. Furthermore, these valves are relatively inert. Since the pressurized air in haemo-dynamometers is reduced only in small steps, a quick-responding valve is desirable. The moving armature is often located in the flow channel of the medium to be controlled, which makes the valve susceptive to fouling.